Production of scratch-resistant polycarbonate moulded parts

ABSTRACT

Method for coating the surface of polycarbonate moulded parts, with a polycarbonate based on a diphenol of formula (Ia) ##STR1## wherein R 1 , R 2 , R 3 , X and m are defined herein, and a material (b), which has been obtained by hydrolytic polycondensation of an aluminum compound of an organofunctional silane and an oxide component.

BACKGROUND OF THE INVENTION

Moulded parts made from polycarbonates are distinguished bytransparency, high impact strength, high heat deflection temperature anddimensional stability. However their susceptibility to scratching oftendetracts from these qualities. In order to remedy this, the mouldedparts can be provided beforehand with a scratch-resistant layer. Thescratch-resistant coatings or coating methods used hitherto are stillnot completely satisfactory particularly as regards scratch resistanceand adhesion of the layer to the substrate with the lowest possiblelayer thickness or curing time of the scratch-resistant layers.

The invention relates to a method for coating particular polycarbonateshaving a high heat deflection temperature using particularsiloxane-containing coatings, wherein the resulting coating has aparticularly high scratch resistance and good adhesion to the substrateand the coating cures within a short period and exhibits a particulartransparency.

SUMMARY OF THE INVENTION

The invention provides a method for coating polycarbonate moulded parts,which is characterised in that to the surface of a moulded body composedof a polycarbonate based on a diphenol of formula (Ia) ##STR2## whereinR¹ and R² independently of one another signify hydrogen, halogen,preferably chlorine or bromine, C₁ -C₈ alkyl, C₅ -C₆ cycloalkyl, C₆ -C₁₀aryl, preferably phenyl, and C₇ -C₁₂ aralkyl, preferably phenyl-C₁ -C₄alkyl, in particular benzyl,

m signifies 4 or 5,

R³ and R⁴ are individually selectable for each X and independently ofone another signify hydrogen or C₁ -C₆ alkyl and

X signifies carbon,

with the proviso that, on at least one atom X, R³ and R⁴ simultaneouslysignify alkyl,

a material (b), which has been obtained by hydrolytic polycondensationof an aluminium compound of an organofunctional silane and an oxidecomponent, is applied in a thickness of from 2 to 200 μm and thematerial is cured at a temperature of from 135° to 180° C.

The invention also provides the scratch-resistant polycarbonate mouldedbodies thus obtained.

The polycarbonates A are high-molecular, thermoplastic, aromaticpolycarbonates having molecular weights M_(w) (weight average) of atleast 10,000, preferably of from 20,000 to 300,000, which contain thebifunctional carbonate structural units of formula (I) ##STR3## whereinR¹ and R² independently of one another signify hydrogen, halogen,preferably chlorine or bromine, C₁ -C₈ alkyl, C₅ -C₆ cycloalkyl, C₆ -C₁₀aryl, preferably phenyl, and C₇ -C₁₂ aralkyl, preferably phenyl-C₁ -C₄alkyl, in particular benzyl,

m signifies 4 or 5,

R³ and R⁴ are individually selectable for each X and independently ofone another signify hydrogen or C₁ -C₆ alkyl and

X signifies carbon,

with the proviso that, on at least one atom X, R³ and R⁴ simultaneouslysignify alkyl.

PREFERRED EMBODIMENTS

These polycarbonates and the underlying dihydroxydiphenylcycloalkanes offormula (Ia) and the preparation of both products are described indetail in EP 395 953. The dihydroxydiphenylcycloalkanes of formula (Ia)are starting materials for the polycarbonates A. In this formula (Ia)the preferred alkyl radical is methyl; the X atoms in the α-position tothe diphenyl-substituted C atom (Cl) are preferably notdialkyl-substituted, whereas alkyl disubstitution in the β-position toCl is preferred.

Dihydroxydiphenylcycloalkanes having rings of 5 and 6 C atoms in thecycloaliphatic radical (m=4 or 5 in formula Ia) are preferred, forexample the diphenols of formulae (Ib) to (Id) ##STR4## with the1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (formula Ib havingR¹ and R² equal to H) being particularly preferred.

One diphenol of formula (Ia) may be used, with the formation ofhomopolycarbonates, or several diphenols of formula (Ia) may be used,with the formation of copolycarbonates.

Furthermore the diphenols of formula (Ia) may also be used mixed withother diphenols, for example with those of formula (Ie)

    HO--Z--OH                                                  (Ie)

for the preparation of high-molecular, thermoplastic, aromaticpolycarbonates.

Other suitable diphenols of formula (Ie) are those wherein Z is anaromatic radical having 6 to 30 C atoms, which can contain one or morearomatic rings, can be substituted and can contain as bridges aliphaticradicals or cycloaliphatic radicals different from those in formula (Ia)or hetero atoms.

Particularly preferred diphenols of formula (Ie) are, for example:

2,2-bis(4-hydroxyphenyl)propane,2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane,2,2-bis(3,5-dichloro-4-hydroxyphenyl)propane,2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane and1,1-bis(4-hydroxyphenyl)-cyclohexane. They can be used both individuallyand as mixtures.

The molar ratio of diphenols of formula (Ia) to the other diphenols offormula (Ie) optionally used concomitantly is to be between 100 mol-% of(Ia) to 0 mol-% of (Ie) and 2 mol-% of (Ia) to 98 mol-% of (Ie),preferably between 100 mol-% of (Ia) to 0 mol-% of (Ie) and 5 mol-% of(Ia) to 95 mol-% of (Ie), particularly between 100 mol-% of (Ia) to 0mol-% of (Ie) and 10 mol-% of (Ia) to 90 mol-% of (Ie), and mostparticularly between 100 mol-% of (Ia) to 0 mol-% of (Ie) and 20 mol-%of (Ia) to 80 mol-% of (Ie).

The high-molecular polycarbonates made from the diphenols of formula(Ia), optionally in combination with other diphenols, can be prepared byall the known methods for the preparation of polycarbonates. Here thedifferent diphenols can be linked to one another both statistically andin blocks.

The polycarbonates can be branched in a manner known per se bycondensing small quantities, preferably quantities of between 0.05 and2.0 mol-% (referred to diphenols used), of trifunctional or more thantrifunctional compounds, particularly those having three or more thanthree phenolic hydroxyl groups. Examples of some branching agents havingthree or more than three phenolic hydroxyl groups are:

phloroglucinol, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)-heptene-2,4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptane,1,3,5-tri(4-hydroxyphenyl)benzene, 1,1,1-tri(4-hydroxyphenyl)ethane,tri(4-hydroxyphenyl)phenylmethane, 2,2-bis4,4-bis(4-hydroxyphenyl)cyclohexyl!propane,2,4-bis(4-hydroxyphenylisopropyl)phenol,2,6-bis(2-hydroxy-5-methylbenzyl)-4-methylphenol,2-(4-hydroxyphenyl)-2-(2,4-dihydroxyphenyl)propane, hexa4-(4-hydroxyphenylisopropyl)phenyl!orthoterephthalate,tetra(4-hydroxyphenyl)methane, tetra4-(4-hydroxyphenylisopropyl)phenoxy!methane and 1,4-bis4,4"-dihydroxytriphenyl)methyl!benzene.

Some other trifunctional compounds are 2,4-dihydroxybenzoic acid,trimesic acid, cyanuric chloride and3,3-bis(3-methyl-4-hydroxyphenyl)-2-oxo-2,3-dihydroindole.

Monofunctional compounds are used in conventional concentrations aschain stoppers for the known per se control of the molecular weight ofthe polycarbonates A. Suitable compounds are, for example, phenol, tert.-butylphenols or other alkyl-C₁ -C₇ -substituted phenols. Smallquantities of phenols of formula (If) ##STR5## wherein R represents abranched C₈ alkyl and/or C₉ alkyl radical are particularly suitable forcontrolling the molecular weight.

In the alkyl radical R the proportion of CH₃ protons is preferablybetween 47 and 89% and the proportion of CH-- and CH₂ protons ispreferably between 53 and 11%; also R is preferably in the o-positionand/or p-position to the OH group, and particularly preferably the upperlimit of the ortho-proportion is 20%. The chain stoppers are employedgenerally in quantities of from 0.5 to 10 mol-%, preferably from 1.5 to8 mol%, referred to the diphenols used.

For further details reference is made to EP 395 953.

The polycarbonates A can be prepared by the known method in homogeneousphase, by the so-called "pyridine method" as well as by the known melttransesterification method using, for example, diphenyl carbonateinstead of phosgene.

The polycarbonates have a high heat deflection temperature owing to theincorporation of diphenols of formula (Ia).

The particularly preferred polycarbonates A are those containing unitsof the formula (Ig) ##STR6## wherein R¹ and R² have the meanings givenfor formula (I), but which are particularly preferably hydrogen.

In addition to a high heat deflection temperature, the polycarbonateshave a good UV-stability and good flow properties in the melt.

Through the optional combination with other diphenols, particularly withthose of formula (Ie), the properties of the polycarbonates may moreoverbe varied advantageously. In copolycarbonates of this kind, thediphenols of formula (Ia) are contained in the polycarbonates inquantities of from 100 mol-% to 2 mol-%, preferably in quantities offrom 100 mol-% to 5 mol%, particularly in quantities of from 100 mol-%to 10 mol-% and most particularly from 100 mol-% to 20 mol-%, referredto the total quantity of 100 mol-% of diphenol units.

The scratch-resistant coatings B are obtained by hydrolyticprecondensation, optionally in the presence of a condensation catalystcomposed of

a) at least one organofunctional silane of formula (I)

    R'.sub.m SIX.sub.(4-m)                                     (I)

wherein the groups X, which can be identical or different, signifyhydrogen, halogen, alkoxy, acyloxy, alkylcarbonyl, alkoxycarbonyl orNR"₂ (R" represents H and/or alkyl) and the radicals R', which can beidentical or different, represent alkyl, alkenyl, alkinyl, aryl,arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, arylalkinyl oralkinylaryl, wherein these radicals can be interrupted by O atoms or Satoms or the group --NR" and can carry one or more substituentscomprising the halogen group and the optionally substituted amino,amide, aldehyde, keto, alkylcarbonyl, carboxy, mercapto, cyano, hydroxy,alkoxy, alkoxycarbonyl, sulphate, phosphate, acryloxy, methacryloxy,epoxy or vinyl groups, and m has the value 1, 2 or 3, and/or an oligomerderived from these, in a quantity of from 25 to 95 mol-%, referred tothe total number of moles of the (monomeric) starting components;

b) at least one aluminium compound of the empirical formula (II)

    AlR.sub.3                                                  (II)

wherein the radicals R, which can be identical or different, signifyhalogen, alkyl, alkoxy, acyloxy or hydroxy, while the groups justmentioned can be wholly or partly replaced by chelating ligands, and/oran oligomer derived therefrom and/or an optionally complexed aluminiumsalt of an inorganic or organic acid, in a quantity of from 5 to 75mol-%, referred to the total number of moles of the (monomeric) startingcomponents; and optionally

c) one or more oxides, which are soluble in the reaction medium and oflow volatility, of an element from the main groups Ia to Va or from thesubgroups IIb, IIIb, Vb to VIIIb of the periodic table, with theexception of Al, and/or one or more compounds of one of these elements,which compounds are soluble in the reaction medium and under thereaction conditions form an oxide of low volatility, in a quantity offrom 0 to 70 mol-%, referred to the total number of moles of the(monomeric) starting components; using a quantity of water smaller thanthe quantity stoichiometrically required for the complete hydrolysis ofthe hydrolysable groups, either

i) further condensation is carried out by adding further water, whichwholly or partly brings about the hydrolysis of the remaininghydrolysable groups, and optionally a condensation catalyst, followed byapplication to the substrate or subjection to a moulding process; and/or

ii) application to the substrate or subjection to a moulding process iscarried out, and then further condensation in an atmosphere containingwater vapour.

The following are appropriate for the general formulae given above:alkyl radicals, for example, straight-chain, branched or cyclic radicalshaving 1 to 20, preferably 1 to 10, carbon atoms and particularly loweralkyl radicals having 1 to 6, preferably 1 to 4 carbon atoms. Particularexamples are methyl, ethyl, n-propyl, isopropyl, n-butyl, sec. butyl,tert. butyl, isobutyl, n-pentyl, n-hexyl, dodecyl, octadecyl andcyclohexyl.

Examples of alkenyl radicals and alkinyl radicals are straight-chain,branched or cyclic radicals having 2 to 20, preferably 2 to 10 carbonatoms and at least one C--C double or triple bond and in particularlower alkenyl radicals and alkinyl radicals such as vinyl, allyl,2-butenyl, ethinyl and propargyl.

The alkoxy, acyloxy, alkylamino, dialkylamino, alkylcarbonyl,alkoxycarbonyl, alkylaryl, arylalkyl, alkenylaryl, arylalkenyl,alkinylaryl, arylalkinyl radicals and the substituted amino radicals oramide radicals can be derived for example, from the above-mentionedalkyl, alkenyl and alkinyl radicals. Particular examples are methoxy,ethoxy, n-propoxy and i-propoxy, n-butoxy, sec. and tert. butoxy,isobutoxy, β-methoxyethoxy, acetyloxy, propionyloxy, monomethylamino,monoethylamino, dimethylamino, diethylamino, N-ethylanilino,methylcarbonyl, ethylcarbonyl, methoxycarbonyl, ethoxycarbonyl, benzyl,2-phenylethyl, tolyl and styryl. Preferred aryl radicals are phenyl,hydroxyphenyl, biphenyl and naphthyl, with phenyl being particularlypreferred.

The said radicals may optionally carry one or more substituents, forexample, halogen atoms, lower alkyl or alkoxy radicals and nitro groups.Here halogen atoms (for example, F, Cl, Br) are preferred, particularlyfluorine atoms, which can impart to the end product hydrophobicproperties and particularly good resistance to condensed water. In thisconnection halogenated, particularly fluorinated, silanes have proved tobe particularly advantageous.

Of the halogens which are bonded directly to the central atom, fluorine,chlorine and bromine are preferred. Chlorine is particularly preferred.

Aluminium compounds which can be used according to the invention are inparticular those of the empirical formula

    AlR.sub.3                                                  (II)

wherein the radicals R, which can be identical or different, signifyhalogen, in particular Cl and/or Br, alkyl, alkoxy, acyloxy or hydroxy,while the groups just mentioned can be wholly or partly replaced bychelating ligands. The presence of a chelating ligand is particularlypreferred when two or three identical radicals R result in a compoundAlR₃ which is very reactive towards H₂ O, and the control of thehydrolysis reaction and the avoidance of precipitates is therebyrendered more difficult. Examples of such radicals R are halogen andalkyl. The use of a chelating ligand is also of advantage when R is OH.Acetylacetone and ethyl acetoacetate, for example, are possiblechelating ligands.

Salts of inorganic and organic acids such as, for example, HNO₃, H₂ SO₄,H₃ PO₄ and formic acid, acetic acid, propionic acid and oxalic acid canalso be used according to the invention. In this case complexing bymeans of a chelating ligand is also recommended.

Specific examples of aluminium compounds which can be used according tothe invention are Al(OCH₃)₃, Al(OC₂ H₅)₃, Al(O--n--C₃ H₇)₃, Al(O--i--C₃H₇)₃, Al(OC₄ H₉), Al(O--i--C₄ H₉)₃, Al(O--sec.--C₄ H,)₃, AlCl₃,AlCl(OH)₂, aluminium formate, aluminium acetate and aluminium oxalate aswell as the corresponding (partly) chelated compounds such as, forexample, the acetylacetonates. Compounds which are liquid at roomtemperature such as, for example, Al(O--sec.--C₄ H₉)₃ and Al(O--i--C₃H₇)₃, are particularly preferred.

In the organofunctional silanes the group R' can optionally beinterrupted by atoms of oxygen or sulphur or by --NR"-- groups.

Specific examples of suitable organofunctional silanes are:

CH₃ --Si--Cl₃, CH₃ --Si--(OC₂ H₅)₃, C₂ H₅ --Si--Cl₃, C₂ H₅ --Si--(OC₂H₅)₃,

CH₂ =CH--Si--(OC₂ H₅)₃, CH₂ =CH--Si--(OC₂ H₄ OCH₃)₃,

CH₂ =CH--Si--(OOCCH₃)₃, CH₂ =CH--SiCl₃, CH₂ =CH--CH₂ --Si--(OCH₃)₃,

CH₂ =CH--CH₂ --Si--(OC₂ H₅)₃, C₃ H₇ --Si--(OCH₃)₃, C₆ H₅ --Si--(OCH₃)₃,

C₆ H₅ --Si--(OC₂ H₅)₃, (CH₃)₂ --Si--Cl₂, (CH₃)₂ --Si--(OC₂ H₅)₂,

(C₂ H₅)₂ --Si--(OC₂ H₅)₂, (CH₃) (CH₂ =CH)--Si--Cl₂,

(CH₃)₃ --Si--Cl, (C₂ H₅)₃ --Si--Cl, (CH₃)₂ --Si--(OCH₃)₂,

(CH₃)₂ --Si--(OC₂ H₅)₂, (C₆ H₅)₂ --Si--Cl₂, (C₆ H₅)₂ --Si--(OCH₃)₂,

(C₆ H₅)₂ --Si--(OC₂ H₅)₂, (t--C₄ H₉), (CH₃)₂ --Si--Cl,

(CH₃)₂ --(CH₂ =CH--CH₂)--Si--Cl, (CH₃ O)₃ --Si--C₃ H₆ --Cl,

(C₂ H₅ O)₃ --Si--C₃ H₆ --CN, ##STR7## (CH₃ O)₃ --Si--C₃ H₆ --NH₂, (C₂ H₅O)₃ --Si--C₃ H₆ --NH₂,

(C₂ H₅ O)₂ (CH₃)--Si--C₃ H6--NH₂, H₂ N--CH₂ --CH₂ --NH--C₃ H₆--Si--(OCH₃)₃,

H₂ N--CH₂ --CH₂ --NH--CH₂ --CH₂ --C₃ H₆ --Si--(OCH₃)₃, ##STR8##

Some of these silanes are commercial products, or they can be preparedby known methods; cf. W. Noll, "Chemie und Technologie der Silicone",Verlag Chemie GmbH, Weinheim/Bergstraβe (1968).

In the silanes of the general formula (I) the index m preferablyequals 1. At higher values of m there is the risk that the hardness ofthe material will decrease if an excessive amount of such a silane isused. Accordingly as a rule the best results are obtained when at least60 mol-%, particularly at least 75 mol-%, and most preferably at least90 mol-%, with reference to the total number of moles of silanes offormula (I) used, are silanes wherein m in formula (I) equals 1. Thequantity of silanes of formula (I) wherein m equals 3 is preferably notmore than 5 mol-% of the silanes used. Particularly preferred silanesfor the present invention are γ-glycidyl oxypropyltrialkoxysilanes,γ-aminopropyltrialkoxysilanes, propyltrialkoxysilanes,phenyltrialkoxysilanes, vinyltrialkoxysilanes and mixtures thereof. Inthese compounds "alkoxy" preferably means methoxy or ethoxy.

Instead of the monomeric starting silanes, precondensed oligomers ofthese silanes which are soluble in the reaction medium can alsooptionally be used; that is, straight-chain or cyclic, low-molecularpartial condensates (polyorganosiloxanes) having a degree ofcondensation, for example, of from about 2 to 100, particularly of about2 to 6. This applies similarly to the aluminium component (b) and thecomponent (c). It is also possible optionally to use an oligomerpossessing central atoms differing from one another.

Compounds used as component c) are oxides which are soluble in thereaction medium and of low volatility, or compounds which form suchoxides of low volatility, of elements from the main groups Ia to Va orfrom the subgroups IIb, IIIb, Vb to VIIIb of the periodic table, withthe exception of aluminium. The component c) is preferably derived fromthe following elements: alkaline earth metals, such as Mg and Ca, B, Si,Sn, Pb, P, As, Sb, Bi, Cr, Mo, W, Mn, Fe, Co, Ni, Zn and/or V, with B,Si, Sn, Zn and P being particularly preferred. The lanthanides andactinides may also optionally be used.

Particularly preferred oxides of low volatility are B₂ O₃, P₂ O₅ andSnO₂.

Examples of compounds which form oxides which are soluble in thereaction medium and of low volatility are inorganic acids, such asphosphoric acid and boric acid, and esters thereof. Also suitable are,for example, halides such as SiCl₄, HSiCl₃, SnCl₄ and PCl₅ and alkoxidessuch as Ca(OR)₂, Si(OR)₄, Sn(OR)₄ and VO(OR)₃, wherein R is derived fromlower alcohols such as methanol, ethanol, propanol or butanol. Otherstarting compounds which can be used are corresponding salts of volatileacids, for example, acetates such as silicon tetraacetate, basicacetates such as basic lead acetate and formates.

To prepare the composition according to the invention there arepreferably used from 40 to 90, particularly 40 to 80, and particularlypreferably 70 to 80 mol-% of component (a), from 10 to 40, particularly10 to 30, and particularly preferably 15 to 25 mol-% of component (b)and 50 mol-% at most, in particular 40 mol-% at most of component (c).

To prepare the coating, the starting components are precondensed in thedesired mixing ratio using a quantity of water smaller than the quantitystoichiometrically required for the complete hydrolysis of all thehydrolysable groups used. This substoichiometric quantity of water ispreferably added in such a way that local excess concentrations andprecipitates caused thereby (for example, of Al₂ O₃ . xH₂ O) areavoided. This can be done, for example, by introducing the quantity ofwater into the reaction mixture with the assistance of moisture-ladenadsorbents, for example, silica gel or molecular sieves, hydrous organicsolvents, for example, 800 ethanol, or hydrated salts, for example,CaCl₂ . 6H₂ O. Another method is to introduce the water through a systemcontaining components which react with one another and thereby slowlyliberate water, as is the case, for example, in the formation of anester from an alcohol and an acid (ccc, or chemically controlledcondensation).

The precondensation is preferably carried out in the presence of acondensation catalyst. Optionally, in particular when one of thecomponents (a) to (c) is highly nonpolar (for example, a silane whereinR' represents aryl), an organic solvent which is at least partlymiscible with water can be employed, for example, an aliphatic alcoholsuch as ethanol, propanol, isopropanol or butanol, an ether such asdimethoxyethane, an ester such as dimethyl glycol acetate, or a ketonesuch as acetone or methyl ethyl ketone. The preferred solvent isn-butanol. It may be preferable not to evaporate off the solvent addedor formed during the precondensation, but to use the reaction mixture asit is for the further condensation.

Suitable condensation catalysts are compounds which abstract protons andhydroxyl ions, and amines. Particular examples are organic or inorganicacids, such as hydrochloric acid, sulphuric acid, phosphoric acid,formic acid or acetic acid, as well as organic or inorganic bases, suchas ammonia, alkali metal hydroxides or alkaline earth metal hydroxides,for example, sodium hydroxide, potassium hydroxide or calcium hydroxide,and amines soluble in the reaction medium, for example, loweralkylamines or alkanolamines. In this connection volatile acids andbases, in particular hydrochloric acid, ammonia and triethylamine areparticularly preferred. The total concentration of catalyst can be, forexample, up to 3 mol/liter.

It is especially advantageous if one of the reaction components (a) to(c) already acts as a condensation catalyst. Here particular mention maybe made of the silanes (a) possessing one or more radicals R' which aresubstituted with basic groups, for example, --NH₂. Thus theaminoalkylsilanes, for example, have proved very successful for thesepurposes. Specific examples of such compounds are γ-aminopropylsilanes,in particular γ-aminopropyl-tri(m)ethoxysilane. The use of suchcompounds as reaction components has the additional advantage that adecided improvement in the adhesion of the composition to varioussubstrates, for example, plastics, metal, glass, and simultaneously adistinct increase in scratch resistance and abrasion resistance can beobserved thereby. Reaction components of this kind which act ascondensation catalysts can be used either alone or in combination withthe conventional condensation catalysts mentioned above.

The precondensation is usually carried out at temperatures of from -20°to 100° C., preferably of from 0° to 30° C. When an organic solvent isused, the precondensation can also take place at temperatures of up tothe boiling point of the solvent, but here also it is preferably carriedout at between 0° and 30° C.

Optionally one or more starting components, or part of one, more or allof the starting components, can initially be precondensed and then theremaining starting components admixed and subsequently co-condensed bythe process of precondensation or further condensation.

The subsequent hydrolytic further condensation of the precondensate iscarried out in the presence of additional water which wholly or partly,for instance, to the extent of at least 80%, particularly of at least90%, brings about the hydrolysis of the hydrolysable groups stillremaining. It is preferable to use an excess of water, referred to thehydrolysable groups still present. In an embodiment preferred onpractical grounds, the quantity of water used for the furthercondensation is that which would be required stoichiometrically for thecomplete hydrolysis of the starting components employed initially (herethe water already added is thus left out of account).

In order as far as possible to avoid precipitation, the water is addedparticularly preferably in several stages, for example, in three stages.For example, 1/10 to 1/20 of the quantity of water stoichiometricallyrequired for hydrolysis is added in the first stage. 1/5 to 1/10 of thestoichiometric quantity of water is added after brief stirring andfinally, after further brief stirring, a stoichiometric quantity ofwater is added such that ultimately a slight excess of water is present.

The further condensation is carried out preferably in the presence ofone of the above-mentioned condensation catalysts, with volatilecompounds and reaction components (a) likewise being preferred. Thetotal concentration of catalyst can be, for example, up to 5 mol/liter.

In the further condensation, optionally one of the above-mentionedorganic solvents may also be present or may be added, with solventformed during the precondensation or further condensation, or solventwhich may have been added for the precondensation or furthercondensation, preferably not being evaporated off after completion ofthe further condensation.

The precondensate reacts owing to its susceptibility to hydrolysis bywater vapour and can therefore also be further condensed in anatmosphere containing water vapour. In this case the addition to thecondensate of further water can be wholly or partly dispensed with.

The further condensation is usually carried out at temperatures of from-20° to 100° C., preferably of from 0° to 30° C.

Surprisingly, it has become apparent that on heating the compositionobtained to 40° to 80° C. without evaporating off the solvent, itsviscosity is stabilised, that is, the viscosity remains essentiallyconstant for a prolonged period after completion of thepolycondensation.

The composition can be used as it is after precondensation or after thefurther condensation. But conventional additives may optionally beadded, for example, organic thinners, flow-control agents, colouringagents (dyes or pigments), UV stabilisers, fillers, viscositycontrollers, lubricants, wetting agents, antisettling agents orantioxidants.

The processing of the composition must take place within a definite potlife. This pot life depends greatly on the nature and quantity of thecomponents (a) to (c) used and can be, for example, 1 day, or even oneweek or even longer.

For coating purposes the conventional coating methods are employed, forexample, dipping, flow coating, casting, spin-coating, spraying orspreading.

The coating is applied in layer thicknesses of, for example, from 2 to200 μm, preferably from 2 to 30 μm and particularly from 5 to 15 μm.Optionally the substrate can be primed with an adhesion promoter orpriming layer prior to application of the coating according to theinvention.

Curing of the coats is carried out according to the invention attemperatures of above 135° C., preferably of above 150° C.

EXAMPLES

3 mm thick plates (12×5 cm) of commercially available polycarbonates(copolycarbonates based on the diphenol Ib and on bisphenol A, Apec HTKU 1-9350 having Tg=185° C., from the firm Bayer or, for comparison, apolycarbonate based on bisphenol A, Makrolon 3108 having Tg=148° C. fromthe firm Bayer) were purified using isopropanol and were coated with alayer 20 μm thick by being dipped in the scratch-resistant coatingaccording to the invention (Ormocer of ISC Wurzburg of theFraunhofergesellschaft according to EP 0 358 011 A2) at a dipping ratev=100 cm min⁻¹. After being aired for 10 minutes at room temperature,the coated plates were dried at elevated temperatures. The drying timesand drying temperature were varied. The layer thickness of thescratch-resistant coat after drying was 5 μm.

The coated plates, after completion of curing, were stored for 2 days atroom temperature and then subjected to the Taber abrasion method (ASTM D1044). The results of the tests are shown in Table 1.

Taber abrasion method (ASTM D 1044)

The testing apparatus consists of a horizontally arranged plate ontowhich the test piece is fixed. The plate is driven with a rate ofrotation of 55±6 revolutions/minute. Two cylindrical abrasive parts(CS-10.F) are arranged vertically and rotatably so that they grind thesurface of the test piece, each with a loading of 1000 g.

The turbidity caused by the abrasion is measured in accordance with ASTM1003, using a sphere photometer. The turbidity is measured on twosamples at the time of supply and after rotation. The increase inturbidity (difference between final turbidity sand turbidity at the timeof supply) is stated.

Results

Scratch-resistant coatings: Influence of the curing temperature andcuring time in the case of BTMC-BPA copolycarbonate plates

    ______________________________________                                                         Taber abrader                                                                 (Test 4)                                                                      1000 g loading                                                                Grinding roller                                                       Curing            CS 10                                              Curing   time    Plate     Turbidity after                                    (°C.)                                                                           (min)   material  >500 cycles                                                                           1000 cycles                                ______________________________________                                        135      10      A         11.4    19.0                                       150      10      A         5.5     11.5                                       170      10      A         5.3     11.3                                       150      10      A         5.5     11.5                                       150      20      A         5.3     11.5                                       150      30      A         5.2     11.4                                       150      45      A         5.2     11.4                                       Comparison:                                                                   130      10      C         14.2    33.0                                       130      45      C         10.1    17.9                                       130      45      A         9.3     15.4                                       ______________________________________                                         BP TMC = 1,1bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane                   BPA = 2,2bis(4-hydroxyphenyl)propane                                          A = BPTMC/BPA copolycarbonate Tg = 185° C., Apec HT KU 1-9350 from     the firm Bayer                                                                C = BPA polycarbonate Tg = 148° C. Makrolon 3108 from the firm         Bayer                                                                    

What is claimed is:
 1. A method for coating polycarbonate moulded parts, the method comprising the steps of:a) applying a material obtained by hydrolytic polycondensation of an aluminum compound of an organofunctional silane and an oxide compound, in a thickness of from 2 to 200 μm, to a surface of a moulded body comprising a polycarbonate containing diphenol-units in which 2 to 100 mol-% of the diphenol-units correspond to a dihydroxydiphenylcycloalkane of formula (Ia); ##STR9## where R¹ and R², independently of one another, represent hydrogen, halogen, C₁ -C₈ alkyl, C₅ -C₆ cycloalkyl, C₆ -C₁₀ aryl, or C₇ -C₁₂ aralkyl, m is 4 or 5, R³ and R⁴, independently of one another, are individually selectable for each X and represent hydrogen or C₁ -C6 alkyl, and X represents carbon, with the proviso chat on at least one atom X, R³ and R⁴ simultaneously represent alkyl, and b) curing the material at a temperature of between 135° and 180° C.
 2. The method according to claim 1, wherein the halogen group is chlorine or bromine.
 3. The method according to claim 1, wherein the C₆ -C₁₀ aryl group is phenyl.
 4. The method according to claim 1, wherein the C₇ -C₁₂ aralkyl group is phenyl- or benzyl- C₁ -C₄ alkyl.
 5. The method according to claim 1, wherein the dihydroxydiphenylcycloalkane is a compound of formulae (Ib), (Ic), or (Id): ##STR10## R¹ and R² are the same as defined in formula (Ia).
 6. The method according to claim 1, wherein the polycarbonate further contains other diphenol-units in which 0 to 98 mol-% of the other diphenol units correspond to a diphenol of formula (Ie):

    HO--Z--OH (Ie),

where Z represents an aromatic radical having 6 to 30 carbon atoms.
 7. A polycarbonate moulded body comprising:a) a thermoplastic, aromatic polycarbonate having a molecular weight M_(w) of at least 10,000 and containing bifunctional carbonate structural units in which 2 to 100 mol-% of the bifunctional carbonate structural units correspond to a compound of formula (I): ##STR11## (I), where R¹ and R², independently of one another, represent hydrogen, halogen, C₁ -C₈ alkyl, C₅ -C₆ cycloalkyl, C₆ -C₁₀ aryl, or C₇ -C₁₂ aralkyl, m is 4 or 5, R³ and R⁴, independently of one another, are individually selectable for each X and represent hydrogen or C₁ -C₆ alkyl, and X represents carbon, with the proviso that on at least one atom X, R³ and R ⁴ simultaneously represent alkyl, and b) a layer having a thickness of from 2 to 200 μm, the layer being obtained by hydrolytic polycondensation of an aluminum compound of an oganofunctional silane and an oxide compound.
 8. The polycarbonate moulded body according to claim 7, wherein the halogen group is chlorine or bormine.
 9. The polycarbonate moulded body according to claim 7, wherein the C₆ -C₁₀ aryl group is phenyl.
 10. The polycarbonate moulded body according to claim 7, wherein the C₇ -C₁₂ aralkyl group is phenyl- or benzyl- C₁ -C₄ alkyl.
 11. The polycarbonate moulded body according to claim 7, wherein the molecular weight M_(w) of the polycarbonate is between 20,000 and 300,000.
 12. The polycarbonate moulded body according to claim 7, wherein the polycarbonate corresponds to a compound of formula (Ig): ##STR12## where R¹ and R² are the same as defined in formula (I). 